Presently various methods are proposed as methods for connecting information technology devices. A wireless communication using an infrared ray, among others, is widely used because of the advantages (1) through (3) set forth below:
(1) There is no restriction by laws and, thus, it is possible to establish a world-wide universal communication method is possible.
(2) A transmitter/receiver can be small in size, light in weight and low in cost, and the data transmission/reception can be performed with low power consumption.
(3) Linear propagation of light causes no unnecessary information leakage and hardly allows interference. Thus, utilization of space is efficient.
Especially, IrDA (Infrared Data Association) Standard, which is standardized by IrDA (IrDA is an industry organization), defines maximum communication speed to be 4 Mbps. The standard is extensively applied to PCs (personal computers), handy phones, portable information terminals and the like. (Herein, “IrDA Standard” is denoted simply by “IrDA” as generally called.) The IrDA is disclosed in the following Document 1.
[Document 1]
Infrared Data Association, Serial Infrared Link Access Protocol (Version 1.1), Published on Jun. 16, 1996
According to the IrDA, communication protocols have a layered structure. The communication protocols include a SIR (Serial Infrared) layer, an IrLAP (IrDA Link Access Protocol) layer, an IrLM-LMP (IrDA Link Management Protocol) layer and the like. The SIR layer provides a physical rule. The IrLAP layer establishes a transmission channel. IrLM-LMP (i) performs communication processing of an application that operates in a multi-task environment and (ii) transmits a characteristic and a function of a communication-counter part device.
The IrLAP layer is based on a half duplex procedure of a HDLC (a High level Data Link Control) defined by the ISO (International Organization for Standardization). In order to establish a transmission channel of high quality, the IrLAP layer performs following operations.
[Connectionless-Type Service]
                The IrLAP layer searches a device(s) present in a region within a communication range and obtains an address(es) of the device(s) in the region within the communication range.        In the case where plural devices have the same addresses, the IrLAP layer applies a method (means) for dissolving the overlap of the addresses so that each of the devices in the region within the communication range respectively has an address specific thereto.        The IrLAP layer performs broadcast to all devices in the region within the communication range.[Connection-Type Service]        The IrLAP layer establishes a transmission channel (connection) to connect a device, to which the IrLAP layer belongs, with another device that is a target of the connection.        When the connection is being established, the IrLAP layer negotiates communication speed information, data size in a frame transmitted after establishment of the connection, and the like.        The IrLAP layer adds a sequence number to each frame of data to be transmitted and guarantees an order of the sequence.        The IrLAP layer performs transmission error detection and recovery control, thereby guaranteeing data transmission of high reliability.        When a receiver becomes too busy to receive data, the IrLAP layer requests busy control to a sender and restricts transmission of frames.        The layer releases the established connection.        
Moreover, the IrLMP layer (IrLM-LMP layer) includes a LM-MUX (IrLMP Multiplexer) layer and a LN-IAS (LrLMP Information Access Service) layer. The LM-MUX layer supports the communication between applications and performs following operations:
[Processes Performed By LM-MUX Layer]
                By controlling the IrLAP layer, the LM-MUX layer searches a device(s) present in the region within the communication range.        By controlling the IrLAP layer, the LM-MUX layer establishes a transmission channel connecting a device, to which the IrLAP layer belongs, with another device that is a target of the connection.        The LM-MUX layer adds a header to transmission data, thereby clarifying the sender at the receiver.        The LM-MUX layer allots received data according to where the data is to be forwarded, and forwards the data to an upper application to which the data is to be forwarded.        The layer performs exclusive access control and multiplex control.        The LM-MUX layer releases the connections via the IrLAP layer.        
The LN-IAS layer performs a process for transmitting, to the application, information on a characteristic and a function of the communication-counterpart device. This allows the upper application to communicate with a device suitable for a specific purpose such as storing data, printing data or the like.
By the processes explained above, the IrDA makes it possible to dynamically discover a communicable device(s) present in the region within the communication range and to easily provide a communication environment suitable for each application.
The IrDA can easily provide a communication environment according to each application by carrying out the processes. This broadens a range of application usage.
However, communication speed for searching a device(s), identifying the device(s) and negotiating with the device(s), is defined to be relatively low. Moreover, a waiting time accompanies these processes. As the result, these processes become causes of increase in time for communication processing as a whole.